US12542530B2 - Acoustic wave device, filter, branching apparatus, and communication device - Google Patents

Acoustic wave device, filter, branching apparatus, and communication device

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US12542530B2
US12542530B2 US18/578,935 US202218578935A US12542530B2 US 12542530 B2 US12542530 B2 US 12542530B2 US 202218578935 A US202218578935 A US 202218578935A US 12542530 B2 US12542530 B2 US 12542530B2
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electrode fingers
region
acoustic
electrode
velocity
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US20240322785A1 (en
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Tomio Kanazawa
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Kyocera Corp
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Kyocera Corp
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02992—Details of bus bars, contact pads or other electrical connections for finger electrodes
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02543—Characteristics of substrate, e.g. cutting angles
    • H03H9/02574—Characteristics of substrate, e.g. cutting angles of combined substrates, multilayered substrates, piezoelectrical layers on not-piezoelectrical substrate
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/02535—Details of surface acoustic wave devices
    • H03H9/02818—Means for compensation or elimination of undesirable effects
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14544—Transducers of particular shape or position
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/02—Details
    • H03H9/125—Driving means, e.g. electrodes, coils
    • H03H9/145—Driving means, e.g. electrodes, coils for networks using surface acoustic waves
    • H03H9/14544—Transducers of particular shape or position
    • H03H9/1457—Transducers having different finger widths
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/25—Constructional features of resonators using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/46—Filters
    • H03H9/64—Filters using surface acoustic waves
    • H03H9/6423—Means for obtaining a particular transfer characteristic
    • H03H9/6433—Coupled resonator filters
    • H03H9/6483—Ladder SAW filters
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H9/00—Networks comprising electromechanical or electro-acoustic elements; Electromechanical resonators
    • H03H9/70—Multiple-port networks for connecting several sources or loads, working on different frequencies or frequency bands, to a common load or source
    • H03H9/72—Networks using surface acoustic waves

Definitions

  • the present disclosure relates to an acoustic wave device capable of at least one out of converting acoustic waves to electrical signals and converting electrical signals to acoustic waves, a filter including the acoustic wave device, a splitter including the filter, and a communication device including the splitter.
  • a known acoustic wave device includes a piezoelectric layer and an interdigital transducer (IDT) electrode positioned on the piezoelectric layer (for example, Patent Literature 1 listed below).
  • the IDT electrode includes a pair of comb electrodes.
  • Each comb electrode includes a busbar and multiple electrode fingers extending parallel to each other from the busbar.
  • the pair of comb electrodes are disposed so as to mesh with each other.
  • the region where the multiple electrode fingers of one comb electrode and the multiple electrode fingers of the other comb electrode overlap in the direction in the propagation direction of acoustic waves is called a crossing region or the like, and plays an important role in the propagation of acoustic waves.
  • the crossing region includes low-acoustic-velocity regions on both sides in the direction in which the multiple electrode fingers extend and a high-acoustic-velocity region in the center in the direction in which the multiple electrode fingers extend.
  • the acoustic velocity in the low-acoustic-velocity regions is lower than the acoustic velocity in the high-acoustic-velocity region.
  • an acoustic wave device includes a piezoelectric body having a first surface and an IDT electrode positioned on the first surface.
  • the IDT electrode includes multiple first electrode fingers and multiple second electrode fingers.
  • the multiple second electrode fingers are connected to a different potential from the multiple first electrode fingers and are arranged in an alternating manner with the multiple first electrode fingers in a propagation direction of acoustic waves.
  • the multiple first electrode fingers and the multiple second electrode fingers overlap each other in the propagation direction of acoustic waves.
  • the crossing region includes a first region, a second region, and a third region. The first region is located at tip sides of the multiple first electrode fingers.
  • the second region is located more centrally than the first region in a direction in which the multiple first electrode fingers and the multiple second electrode fingers extend and has a higher acoustic velocity than the first region.
  • the third region is located more centrally than the second region and has a higher acoustic velocity than the second region.
  • a filter in an embodiment of the present disclosure, includes the acoustic wave device and one or more other IDT electrodes located on the first surface, connected to the IDT electrode in a ladder configuration, and constituting a ladder filter.
  • a filter includes the acoustic wave device and one or more other IDT electrodes located on the first surface, arranged in the propagation direction of acoustic waves with respect to the IDT electrode, and constituting a multi-mode filter.
  • a splitter in an embodiment of the present disclosure, includes an antenna terminal, a transmission filter, and a reception filter.
  • the transmission filter and the reception filter are connected to the antenna terminal.
  • At least one out of the transmission filter and the reception filter is constituted by either of the above filters.
  • a communication device in an embodiment of the present disclosure, includes the splitter, an antenna, and an integrated circuit (IC).
  • the antenna is connected to the antenna terminal.
  • the IC is connected to the transmission filter and the reception filter.
  • FIG. 1 is a plan view illustrating the configuration of an acoustic wave device according to a First Embodiment.
  • FIG. 2 is a diagram illustrating an example of a cross section taken along line II-II in FIG. 1 .
  • FIG. 3 is a diagram illustrating another example of a cross section taken along line II-II in FIG. 1 .
  • FIG. 4 is a plan view illustrating the configuration of an acoustic wave device according to a Second Embodiment.
  • FIG. 5 is a sectional view taken along line V-V in FIG. 4 .
  • FIG. 6 is a plan view illustrating the configuration of an acoustic wave device according to a Third Embodiment.
  • FIG. 7 is a plan view illustrating the configuration of an acoustic wave resonator according to an embodiment.
  • FIG. 8 is a circuit diagram schematically illustrating the configuration of a splitter according to an embodiment.
  • FIG. 9 is a block diagram illustrating the configuration of a communication device according to an embodiment.
  • FIG. 10 is a diagram illustrating characteristics of resonators according to a First Comparative Example and a First Practical Example.
  • FIG. 11 is a diagram illustrating characteristics of resonators according to a Second Comparative Example and the First Practical Example.
  • FIG. 12 is a diagram illustrating characteristics of resonators according to first and Second Comparative Examples and a Second Practical Example.
  • FIG. 13 is a diagram illustrating characteristics of resonators according to the first and Second Comparative Examples and a Third Practical Example.
  • FIG. 14 is a diagram illustrating characteristics of resonators according to Fourth to Seventh Practical Examples.
  • any direction may be considered up or down with respect to the acoustic wave device according to the present disclosure.
  • a Cartesian coordinate system consisting of a D1 axis, a D2 axis, and a D3 axis is defined below, and terms such as top surface or bottom surface may be used, with the positive side of the D3 axis being on the upper side.
  • terms such as viewed in plan view or viewed in planar perspective view we mean looking in the D3 direction, unless otherwise noted.
  • the D1 axis is defined as parallel to the propagation direction of acoustic waves propagating along the top surface of a piezoelectric body, which will be described below, the D2 axis is defined as parallel to the top surface of the piezoelectric body and perpendicular to the D1 axis, and the D3 axis is defined as perpendicular to the top surface of the piezoelectric body.
  • FIG. 1 is a plan view illustrating main parts of an acoustic wave device 1 according to an embodiment (hereafter, may be simply referred to as a “device 1 ”). In this figure, a velocity profile of the device 1 is also illustrated, as described later.
  • the device 1 includes, for example, a piezoelectric body 3 (refer to FIG. 2 and so on described later) and an IDT electrode 5 positioned on a top surface 3 a (example of a first surface) of the piezoelectric body 3 .
  • FIG. 1 is a plan view of the top surface 3 a . However, symbols relating to the piezoelectric body 3 and illustration of the outer edge of the top surface 3 a and so on are omitted.
  • Acoustic waves that propagate in the D1 direction through a crossing region R 0 of the piezoelectric body 3 are excited by applying a voltage to the IDT electrode 5 . And/or when acoustic waves propagate in the D1 direction through the crossing region R 0 , charge is generated in the piezoelectric body 3 and a voltage is applied to the IDT electrode 5 .
  • the device 1 may, for example, be included in a resonator and/or a filter that utilizes this kind of conversion between acoustic waves and a voltage (electrical signal).
  • the D1 direction may be referred to as a propagation direction of acoustic waves or a propagation direction, and so on.
  • FIG. 1 On the right-hand side of FIG. 1 , a graph depicting the acoustic velocity profile of the device 1 is illustrated. An axis parallel to the D2 direction in the graph represent the position in the IDT electrode 5 in the D2 direction, and corresponding positions are connected by dotted lines. An axis parallel to the D1 direction represents acoustic velocity V. Along this axis, the right side of FIG. 1 (the +D1 side) corresponds to the side with the higher acoustic velocity.
  • the graph on the right side of FIG. 1 only illustrates the ranking of acoustic velocities in multiple regions.
  • the actual values are not reflected in the absolute values of the acoustic velocity in each region, the difference in acoustic velocity between multiple regions, and the ratio of acoustic velocity between multiple regions.
  • the shape of parts of the IDT electrode 5 is exaggerated, and therefore discrepancies occur between the dimensional ratio of the IDT electrode 5 and the velocity profile, which will be discussed in more detail later.
  • the acoustic velocity in the crossing region R 0 is constant across the entire region.
  • the crossing region R 0 includes a high-acoustic-velocity region in the center in the D2 direction and low-acoustic-velocity regions positioned on both sides of the high-acoustic-velocity region in the D2 direction.
  • two types of regions having different acoustic velocities from each other are formed within the crossing region R 0 .
  • the acoustic wave device 1 in the acoustic wave device 1 according to the embodiment, three or more types of regions having different acoustic velocities from each other are formed within the crossing region R 0 .
  • four types of regions namely, first to fourth regions R 1 to R 4 are formed. In this way, for example, transverse mode spurious can be reduced.
  • the regions where the acoustic velocities are different from each other are realized by using a novel planar shape for the IDT electrode 5 .
  • the rest of the configuration may be realized in various ways, for example, may be realized in known ways.
  • the description of the First Embodiment the description will generally be given in the following order.
  • the IDT electrode 5 will be described using the configuration illustrated in FIG. 1 as an example for matters that may be regarded as being known. However, the description may include a description of a novel configuration without specifically stating that this is the case. In the description of (3) above, the planar shape of the IDT electrode 5 in relation to the velocity profile is described.
  • the IDT electrode 5 is composed of a conductor layer stacked on the top surface 3 a of the piezoelectric body 3 .
  • the IDT electrode 5 includes a pair of comb electrodes 7 .
  • Each comb electrode 7 includes, for example, a busbar 9 and multiple electrode fingers 11 extending parallel to each other from the busbar 9 .
  • the electrode fingers 11 of one comb electrode 7 (the electrode fingers 11 extending from the busbar 9 on the ⁇ D2 side toward the +D2 side in FIG. 1 ) may be referred to as first electrode fingers 11 A.
  • the electrode fingers 11 of the other comb electrode 7 (electrode fingers 11 extending from busbar 9 on +D2 side toward ⁇ D2 side in FIG. 1 ) may be referred to as second electrode fingers 11 B.
  • the pair of comb electrodes 7 is disposed so that multiple electrode fingers 11 mesh with each other (cross each other).
  • the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B are arranged in an alternating manner so as to be inserted between one another.
  • the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B may be arranged in an alternating manner one by one (illustrated example), or may be arranged in an alternating manner in groups of two or more. There may be different parts resulting from so-called thinning or the like.
  • a configuration in which the electrode fingers are arranged in an alternating manner one by one will be taken as an example.
  • the busbars 9 are, for example, formed in a generally long shape having a constant width and extending in a straight line in the propagation direction of acoustic waves (D1 direction).
  • the pair of busbars 9 face each other in a direction (D2 direction) perpendicular to the propagation direction of acoustic waves.
  • the busbars 9 may vary in width or be inclined with respect to the propagation direction of acoustic waves.
  • the multiple electrode fingers 11 have the same shape and dimensions as each other, for example.
  • Each electrode finger 11 is, for example, formed in a generally long shape with the centerline thereof extending in a straight line in a direction (D2 direction) perpendicular to the propagation direction of acoustic waves.
  • the multiple electrode fingers 11 are arranged in the propagation direction. Note that when we say that the electrode fingers are arranged in the propagation direction, a line (not illustrated) connecting the tips (or bases) of the multiple first electrode fingers 11 A (or multiple second electrode fingers 11 B) may be parallel to the propagation direction (illustrated example) or may be not parallel to the propagation direction.
  • the crossing region R 0 need only be configured so that the adjacent electrode fingers 11 overlap each other in the propagation direction.
  • a pitch p of the multiple electrode fingers 11 (for example, the distance between the centers of two adjacent electrode fingers 11 ) is basically constant within the IDT electrode 5 .
  • the IDT electrode 5 may include some parts that are different in terms of the pitch p. Examples of such different parts include, for example, small pitch parts where the pitch p is smaller than that for the majority (for example, 80% or more) of the electrode fingers 11 , large pitch parts where the pitch p is larger than that for the majority of the electrode fingers 11 , and thinned parts where a small number of electrode fingers 11 have been substantially thinned out.
  • the pitch p refers to the pitch of the parts (majority of the multiple electrode fingers 11 ) excluding the different parts described above.
  • the average value of the pitch of the majority of the electrode fingers 11 may be used as the value of the pitch p.
  • the number of electrode fingers 11 may be set as appropriate in accordance with the electrical characteristics and so forth required for the IDT electrode 5 (device 1 ).
  • FIG. 1 is a schematic diagram, and therefore a small number of the electrode fingers 11 are illustrated. In reality, a greater number of electrode fingers 11 may be arranged than is illustrated in the figure. For example, the number of electrode fingers 11 may be 100 or more.
  • FIG. 1 may be considered to be an illustration of an extracted portion of the IDT electrode 5 .
  • each electrode finger 11 faces an edge of the busbar 9 to which the electrode finger 11 is not connected across a gap G1.
  • the lengths of the multiple gaps G1 in the D2 direction are identical to each other, for example.
  • the voltage is applied to the top surface 3 a of the piezoelectric body 3 by the multiple electrode fingers 11 , thereby causing the top surface of the piezoelectric body 3 to vibrate (if the piezoelectric body 3 is relatively thick) or causing the entire piezoelectric body 3 to vibrate (if the piezoelectric body 3 is relatively thin). This causes acoustic waves that propagate along the top surface 3 a to be excited.
  • the multiple acoustic waves excited by the multiple electrode fingers 11 are in phase with each other in a direction (D1 direction) perpendicular to the multiple electrode fingers 11 and the amplitudes of the acoustic waves add together.
  • D1 direction a direction perpendicular to the multiple electrode fingers 11
  • acoustic waves propagating in the D1 direction are most easily excited.
  • a component having a frequency equivalent to the frequency of acoustic waves, whose half wavelength is roughly equal to the pitch p is converted into acoustic waves.
  • acoustic waves when acoustic waves are generated in the region of the top surface 3 a where the pair of comb electrodes 7 are disposed, mainly, acoustic waves propagating in the D1 direction, whose half wavelength is roughly equal to the pitch p, are converted into a voltage through the a principle opposite to that described above.
  • a resonator or filter is realized by using these principles.
  • the pair of comb electrodes 7 are connected to different potentials from each other.
  • the first electrode fingers 11 A and the second electrode fingers 11 B can be regarded as electrode fingers 11 that are connected to different potentials from each other.
  • acoustic waves of any appropriate mode may be utilized.
  • the acoustic waves may be surface acoustic waves (SAWs).
  • SAWs surface acoustic waves
  • Rayleigh waves or leaky waves may be used as the SAWs.
  • the acoustic waves may be Lamb waves propagating through a thin-plate-shaped piezoelectric body.
  • Lamb waves A1-mode Lamb waves, S0-mode Lamb waves, and shear horizontal (SH) Lamb waves may be used.
  • the modes of acoustic waves do not need to be clearly identifiable or distinguishable in this way.
  • the pitch p of the electrode fingers 11 is basically half the wavelength of acoustic waves that have a frequency equivalent to the intended resonant frequency, as described above.
  • An example of the absolute value of the pitch p is greater than or equal to 0.5 ⁇ m and less than or equal to 15 ⁇ m.
  • the length of the electrode fingers 11 may be, for example, greater than or equal to 10p or 20p, and may be less than or equal to 100p or 50p. The above lower and upper limits may be used in combination as appropriate.
  • the thickness of the IDT electrode 5 is, for example, generally constant regardless of the position in a planar direction (direction parallel to D1-D2 plane).
  • the thickness of the conductor layer may be set as appropriate in accordance with the characteristics required for the device 1 .
  • the thickness of the conductor layer may be greater than or equal to 0.04p and less than or equal to 0.20p, and/or greater than or equal to 50 nm and less than or equal to 600 nm.
  • the conductor layer is formed using a metal, for example.
  • the metal may be any suitable metal and, for example, may be aluminum (Al) or an alloy having Al as a main component (Al alloy).
  • the Al alloy is, for example, an Al-copper (Cu) alloy.
  • the conductor layer may be composed of multiple metal layers.
  • the conductor layer may be composed of a relatively thin layer of titanium (Ti) stacked on the top surface 3 a of the piezoelectric body 3 and an Al or Al alloy stacked on the Ti layer. Ti, for example, contributes to strengthening the bond between the Al or Al alloy and the piezoelectric body 3 .
  • the region where the IDT electrode 5 is disposed can be divided into the following three types of regions in the D2 direction based on the configuration of the IDT electrode 5 .
  • the crossing region R 0 in which the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B overlap in propagation direction of acoustic waves.
  • Gap regions RG in which the gaps G1 are positioned.
  • Busbar regions RB in which the busbars 9 are positioned.
  • the crossing region R 0 may be regarded as a region that is interposed between a line (not illustrated) connecting the tips of the multiple first electrode fingers 11 A to each other and a line (not illustrated) connecting the tips of the multiple second electrode fingers 11 B to each other. If the positions of the above lines and so on differ depending on what position within the width of the electrode fingers 11 is used as a reference when assuming lines connecting prescribed parts (for example, the tips) of the multiple electrode fingers 11 , the center lines of the electrode fingers 11 may be used as a reference.
  • the line connecting the tips of the multiple first electrode fingers 11 A and the line connecting the tips of the multiple second electrode fingers 11 B are straight lines that are parallel to each other.
  • the crossing region R 0 has a quadrangular shape. More precisely, the lines connecting the tips are perpendicular to the electrode fingers 11 , and thus, the crossing region R 0 has a rectangular shape with sides parallel to the D1 direction.
  • the rectangle is, for example, a rectangle that is long in the D1 direction, unlike in FIG. 1 .
  • the crossing region R 0 can alternatively be any shape other than a rectangular shape.
  • the crossing region R 0 may be shaped like a parallelogram with the lines connecting the tips being inclined with respect to the D1 direction.
  • the description of the various regions (R 0 , R 1 to R 4 , RG, and RB) in the description of this embodiment may apply to only part of the IDT electrode, in the D1 direction.
  • the line connecting the tips of the multiple first electrode fingers 11 A is a straight line extending across all the first electrode fingers 11 A.
  • the line connecting the tips of the multiple first electrode fingers 11 A may be straight line for only a prescribed number (for example, 10) or more of the first electrode fingers 11 A.
  • the effect achieved in this embodiment may be obtained in only part of the IDT electrode in the D1 direction. Therefore, for example, various regions of the IDT electrode as a whole may extend in the D2 direction in a V-shape or the like.
  • the gap region RG may be considered as a region interposed between the line connecting the tips of the multiple first electrode fingers 11 A (or the multiple second electrode fingers 11 B) and the edge of the busbar 9 opposite the tips of the multiple first electrode fingers 11 A.
  • the gap region RG has a rectangular shape with long sides parallel to the D1 direction.
  • the gap region RG can alternatively be any shape other than a rectangular shape.
  • the crossing region R 0 is shaped like a parallelogram as described above, the gap region RG may be shaped like a parallelogram with four sides that are respectively parallel to the four sides of the crossing region R 0 .
  • the busbar region RB may be regarded as a region interposed between the edge of the busbar 9 on the side where the electrode fingers 11 are located and the opposite edge of the busbar 9 .
  • the busbar region RB has a rectangular shape with long sides parallel to the D1 direction.
  • the busbar region RB can alternatively be any shape other than a rectangular shape.
  • the busbar region RB may be shaped like a parallelogram with four sides parallel to the four sides of the crossing region R 0 .
  • the busbar region RB may be shaped like a trapezoid with the edge on side where the gap region RG is located serving as the bottom.
  • the crossing region R 0 includes the first to fourth regions R 1 to R 4 , which have different acoustic velocities from each other.
  • the term “acoustic velocity” used here may be, for example, the velocity at which the acoustic waves of the mode utilized by the device 1 propagate through the piezoelectric body 3 .
  • the relationship between the magnitudes of the acoustic velocity in the multiple regions is not reversed with the difference in the specific mode of the acoustic waves utilized. Therefore, there is no need to identify which mode the acoustic velocity of the acoustic wave corresponds to.
  • the acoustic velocity of the acoustic waves is affected by the mass of a member (for example, the IDT electrode 5 ) positioned on the top surface 3 a of the piezoelectric body 3 .
  • a member for example, the IDT electrode 5
  • the greater the mass per unit area the lower the acoustic velocity.
  • the thickness of the conductor layer constituting the IDT electrode 5 is constant, the larger the ratio of the area of the conductor layer to the unit area, the larger the mass per unit area. Therefore, the acoustic velocity is lower in regions where the area percentage of the conductor layer constituting the IDT electrode 5 is larger.
  • the width (length in the D1 direction) of the electrode fingers 11 is not constant.
  • the first to fourth regions R 1 to R 4 having different acoustic velocities are formed. These regions are arranged in the order of the first region R 1 , the second region R 2 , the third region R 3 , and the fourth region R 4 from both sides of the crossing region R 0 in the D2 direction toward the center. If these regions are listed in order from the region having the lowest acoustic velocity, the regions are listed in the order of the first region R 1 , the second region R 2 , the third region R 3 , and the fourth region R 4 . In other words, the acoustic velocity increases with increasing proximity to the region in the center.
  • the first regions R 1 are positioned at both sides (specifically, at both ends) of the crossing region R 0 in the D2 direction.
  • the second regions R 2 are positioned more centrally in the crossing region R 0 in the D2 direction than the first regions R 1 (specifically, adjacent to and toward the center from the first regions R 1 ) and have a higher acoustic velocity than the first regions R 1 .
  • the third regions R 3 are positioned more centrally in the crossing region R 0 in the D2 direction than the second regions R 2 (specifically, adjacent to and toward the center from the second regions R 2 ) and have a higher acoustic velocity than the second regions R 2 .
  • the fourth region R 4 is positioned more centrally in the crossing region R 0 in the D2 direction than the third regions R 3 (specifically, adjacent to and toward the center from the second regions R 2 and located centrally in the crossing region R 0 ) and has a higher acoustic velocity than the third regions R 3 .
  • a line connecting points in the center of the length of the crossing region R 0 in the D2 direction is referred to as a center line of the crossing region R 0 .
  • the two first regions R 1 are at the same distance from the center line of the crossing region R 0 (distance in the D2 direction from the center line) and have the same length in the D2 direction as each other. The same can also be said for the two second regions R 2 and the two third regions R 3 .
  • the fourth region R 4 for example, is positioned with the center of the length thereof in the D2 direction on the center line of the crossing region R 0 .
  • the third regions R 3 have longer lengths (widths) in the D2 direction than any of the other regions within the crossing region R 0 .
  • the sum of the widths of the two third regions R 3 may be greater than or equal to 50%, 80%, or 90% of the width of the crossing region R 0 .
  • the size relationship between widths of the other regions within the crossing region R 0 may be set as appropriate. In the illustrated example, in descending order of width, the order is the first region R 1 , the fourth region R 4 , and the second region R 2 .
  • the first to fourth regions R 1 to R 4 each have a rectangular shape with long sides parallel to the D1 direction, for example.
  • the first to fourth regions R 1 to R 4 may alternatively each have a shape other than a rectangular shape.
  • each of the first to fourth regions R 1 to R 4 may have a parallelogram shape having four sides that are parallel to the four sides of the crossing region R 0 .
  • the degrees of difference in velocity and so on between the first to fourth regions R 1 to R 4 may be set as appropriate. For the degree of differences in velocity and so on, see the details of the planar shape of the IDT electrode that affects the velocity (described below).
  • the busbar regions RB have a lower acoustic velocity than the first regions R 1 , in other words, have a lower acoustic velocity than any of the regions constituting the crossing region R 0 .
  • the gap regions RG for example, have a higher acoustic velocity than the fourth region R 4 , in other words, have a higher acoustic velocity than any of the regions constituting the crossing region R 0 . Because the gap regions RG have a higher velocity than the fourth region R 4 , the gap regions RG have a smaller area percentage occupied by the IDT electrode 5 than the fourth region R 4 . However, in FIG.
  • the changes in the width of the electrode fingers 11 are illustrated in an exaggerated manner, and as a result, the gap regions RG are illustrated as having a larger area percentage occupied by the IDT electrode 5 than the fourth region R 4 , which is different from the actual area percentage.
  • the first to fourth regions R 1 to R 4 are specifically realized by the following shape for the electrode fingers 11 .
  • the width (length in the D1 direction) of the parts of the electrode fingers 11 that are positioned in the third regions R 3 is referred to as a standard width.
  • Each electrode finger 11 includes, for example, the following parts in order from the side where tip of the electrode finger 11 is located in the longitudinal direction.
  • a tip-side wider portion 11 a having a larger width than the standard width.
  • a tip-side main portion 11 b having the standard width.
  • a narrower portion 11 c having a smaller width than the standard width.
  • a base-side main portion 11 d having the standard width.
  • a base-side wider portion 11 e having a larger width than the standard width.
  • a base portion 11 f having the standard width.
  • the third region R 3 on the +D2 side consists of the region where the tip-side main portions 11 b of the first electrode fingers 11 A and the base-side main portions 11 d of the second electrode fingers 11 B overlap in the propagation direction.
  • the third region R 3 on the ⁇ D2 side consists of the region where the base-side main portions 11 d of the first electrode fingers 11 A and the tip-side main portions 11 b of the second electrode finger 11 B overlap in the propagation direction.
  • the first region R 1 on the +D2 side consists of the region where the tip-side wider portions 11 a of the first electrode fingers 11 A and the base-side wider portions 11 e of the second electrode fingers 11 B overlap in the propagation direction.
  • the first region R 1 on the ⁇ D2 side consists of the region where the base-side wider portions 11 e of the first electrode fingers 11 A and the tip-side wider portions 11 a of the second electrode fingers 11 B overlap in the propagation direction.
  • the main portions having the standard width overlap each other, whereas in first regions R 1 , the wider portions having a larger width than the standard width overlap each other.
  • the first regions R 1 have a larger area percentage occupied by the IDT electrode 5 than the third regions R 3 . Consequently, the first regions R 1 have a lower acoustic velocity than the third regions R 3 .
  • the base-side wider portions 11 e of the second electrode fingers 11 B extend further toward the ⁇ D2 side (the center of the crossing region R 0 ) than the tip-side wider portions 11 a of the first electrode fingers 11 A.
  • the base-side wider portions 11 e of the second electrode fingers 11 B overlap not only the tip-side wider portions 11 a of the first electrode fingers 11 A, but also parts of the tip-side main portions 11 b of the first electrode fingers 11 A in the propagation direction.
  • the second region R 2 on the +D2 side consists of the region where the base-side wider portions 11 e and the tip-side main portions 11 b overlap.
  • the positions of the +D2-side ends of the tip-side wider portions 11 a of the first electrode fingers 11 A and the +D2-side ends of the base-side wider portions 11 e of the second electrode fingers 11 B for example, roughly coincide with each other.
  • the base-side wider portions 11 e of the first electrode fingers 11 A extend further toward the +D2 side (the center of the crossing region R 0 ) than the tip-side wider portions 11 a of the second electrode fingers 11 B.
  • the base-side wider portions 11 e of the first electrode fingers 11 A overlap in the propagation direction not only the tip-side wider portions 11 a of the second electrode fingers 11 B, but also parts of the tip-side main portions 11 b of the second electrode fingers 11 B.
  • the second region R 2 on the ⁇ D2 side consists of the region where the base-side wider portions 11 e and the tip-side main portions 11 b overlap.
  • the positions of the ⁇ D2-side ends of the tip-side wider portions 11 a of the second electrode fingers 11 B and the ⁇ D2-side ends of the base-side wider portions 11 e of the first electrode fingers 11 A for example, roughly coincide with each other.
  • the main portions having the standard width overlap each other in the propagation direction.
  • the wider portions having a width larger than the standard width overlap each other in the propagation direction.
  • the main portions and the wider portions overlap each other in the propagation direction.
  • the area percentage occupied by the IDT electrode 5 in the second regions R 2 is smaller than that in the first regions R 1
  • the area percentage occupied by the IDT electrode 5 in the second regions R 2 is larger than that in the third regions R 3 . Consequently, the second regions R 2 have a higher acoustic velocity than the first regions R 1 and a lower acoustic velocity than the third regions R 3 .
  • the fourth region R 4 consists of the region where the narrower portions 11 c of the first electrode fingers 11 A and the narrower portions 11 c of the second electrode fingers 11 B overlap each other in the propagation direction.
  • the third regions R 3 the main portions having the standard width overlap each other, whereas in the fourth region R 4 , the narrower portions 11 c having a smaller width than the standard width overlap each other. Therefore, the fourth region R 4 has a smaller area percentage occupied by the IDT electrode 5 than the third regions R 3 . Consequently, the fourth region R 4 has a higher acoustic velocity than the third regions R 3 .
  • the degree to which the width of the narrower portions 11 c is smaller than the width of the main portions is exaggerated, and in reality, the width of the narrower portions 11 c is greater than 1 ⁇ 2 the width of the base portions 11 f (the standard width in the illustrated example).
  • the narrower portions 11 c overlap each other in the propagation direction. Therefore, the gap regions RG have a smaller area percentage occupied by the IDT electrode 5 than the fourth region R 4 .
  • the gap regions RG have a higher acoustic velocity than the fourth region R 4 (and the first to third regions R 1 to R 3 ). However, unlike in the illustrated velocity profile, the gap regions RG may have a lower acoustic velocity than the fourth region R 4 .
  • the busbar regions RB due to the busbars 9 extending in the D1 direction, the area percentage occupied by the IDT electrode 5 in the busbar regions RB is 100%. On the other hand, in the various regions between the pair of busbars 9 , the area percentage of the IDT electrode 5 is less than 100% because the first electrode fingers 11 A and the second electrode fingers 11 B are spaced apart from each other. Therefore, the busbar regions RB have a lower acoustic velocity than any of the other regions within the region where the IDT electrode 5 is disposed.
  • multiple openings arranged in the D1 direction may be formed in the busbars.
  • the area percentage of the IDT electrode in the busbar regions would not be 100%, and consequently, the acoustic velocity in the busbar regions would be higher.
  • this can be considered as a question of which portions of the IDT electrode are defined as the busbars and the busbar regions.
  • the parts of busbars, which contain multiple openings as described above, that are positioned further toward the crossing region R 0 than the multiple openings may be considered as the busbars 9 in an embodiment.
  • Each of the multiple sections ( 11 a to 11 f ) of the electrode fingers 11 extends, for example, through a constant width (in the D1 direction), and this results in steps being formed at the boundaries with the adjacent sections.
  • these steps have relatively short edges that extend roughly parallel to the D1 direction, for example. From another perspective, in the velocity profile, changes in velocity take place step-like manner. In reality, the corners of the steps may be rounded or the short edges may be curved due to machining errors or the like.
  • At least one of the multiple sections ( 11 a to 11 f ) may include a part that extends with a constant width but the width of the part connected to an adjacent section varies so that the step is gradual.
  • the boundaries between adjacent sections do not necessarily need to be clear.
  • the existence of multiple regions (R 1 to R 4 ) is clear in the velocity profile from ranges where the velocity is constant (in the D2 direction), the boundaries between adjacent regions do not necessarily need to be clear.
  • a step, as in the illustrated example, or a bend in the lateral edge of the electrode finger 11 may be formed at a boundary with an adjacent section among the multiple sections ( 11 a to 11 f ), while the width of at least one of the above adjacent sections varies along the entire length of that one section.
  • each section does not need to include a part extending with a constant width.
  • each region does not need to include a range where the velocity is constant (in the D2 direction).
  • each part ( 11 a to 11 f ) of the electrode fingers 11 may be set as appropriate. For example, this is described in more detail below.
  • the tip-side main portion 11 b and the base-side main portion 11 d account for the majority of the length (in the D2 direction) of each electrode finger 11 .
  • the total length of the tip-side main portion 11 b and the base-side main portion 11 d may account for at least 50%, 80%, or 90% of the length of the electrode finger 11 (or the length of the crossing region R 0 in the D2 direction).
  • the lengths of the tip-side main portion 11 b and base-side main portion 11 d are roughly equal to each other.
  • the base-side main portion 11 d is shorter than the tip-side main portion 11 b by the amount by which the base-side wider portion 11 e is longer than the tip-side wider portion 11 a.
  • the term “total length of the tip-side main portion 11 b and base-side main portion 11 d ” may be replaced by the term “length of a part having the standard width within the crossing region R 0 ”.
  • the length of the tip-side main portion 11 b and/or the base-side main portion 11 d may be determined as a result of setting the total length of the electrode finger 11 (or the length of the crossing region R 0 in the D2 direction) and the length of other parts of the electrode finger 11 .
  • the width of the tip-side main portion 11 b and the width of the base-side main portion 11 d are identical to each other and are also equal to the standard width as described previously.
  • the duty ratio of the standard width may be, for example, greater than or equal to 0.40 or 0.45, and less than or equal to 0.60 or 0.55. An appropriate combination of these upper and lower limits may be used.
  • the length of the tip-side wider portion 11 a (in the D2 direction, in other words, the width of the first region R 1 ) may be, for example, greater than or equal to 0.5p, 1.0p, or 1.5p, and less than or equal to 4.0p, 3.0p, or 2.5p. An appropriate combination of these upper and lower limits may be used.
  • the difference between the length of the base-side wider portion 11 e (in the D2 direction) and the length of the tip-side wider portion 11 a (in other words, the width of the second region R 2 ) may be, for example, greater than or equal to 0.1p or 0.3p, and less than or equal to 1p or 0.7p. An appropriate combination of these upper and lower limits may be used.
  • the width of the second regions R 2 may be, for example, greater than or equal to 0.1 or 0.2 times the width of the first regions R 1 , and may be less than 1 times or less than or equal to 0.5 or 0.3 times the width of the first regions R 1 .
  • An appropriate combination of these upper and lower limits may be used.
  • the width of the second regions R 2 is less than the width of the first regions R 1 , but the width of the second regions R 2 may be greater than or equal to the width of the first regions R 1 .
  • the width of the tip-side wider portion 11 a (in the D1 direction) and the width of the base-side wider portion 11 e are identical to each other for example. However, these widths may be different from each other.
  • the duty ratio of the width of these wider portions may be, for example, greater than or equal to 0.50, 0.55, or 0.60, and may be less than or equal to 0.80, 0.75, or 0.70, provided that the duty ratio is greater than the duty ratio of the standard width. An appropriate combination of these upper and lower limits may be used.
  • the width of the wider portions may be, for example, greater than or equal to 1.1 or 1.2 times the standard width and may be less than or equal to 1.5 or 1.4 times the standard width. An appropriate combination of these upper and lower limits may be used.
  • the length of the narrower portions 11 c (in the direction of D2, in other words, the width of the fourth region R 4 ) may be, for example, greater than or equal to 0.2p, 0.5p, or 0.7p, and may be less than 3.0p, 1.5p, or 1.0p. An appropriate combination of these upper and lower limits may be used.
  • the duty ratio of the width (in the D1 direction) of the narrower portions 11 c may be, for example, greater than or equal to 0.10, 0.30, or 0.35 and less than or equal to 0.50 or 0.45, provided that the duty ratio of the narrower portions 11 c is less than the duty ratio of the standard width.
  • An appropriate combination of these upper and lower limits may be used.
  • the width of the narrower portions 11 c may be, for example, greater than or equal to 0.50, 0.70, or 0.75 times the standard width and less than or equal to 0.95, 0.90, or 0.85 times the standard width. An appropriate combination of these upper and lower limits may be used.
  • the length of the base portions 11 f (in the D2 direction, in other words, the width of the gap regions RG) may be, for example, greater than or equal to 0.1p, 0.2p, or 0.3p and may be less than or equal to 1.0p, 0.7p, or 0.5p. An appropriate combination of these upper and lower limits may be used.
  • the width of the base portions 11 f (in the D1 direction) is, for example, the standard width (in other words, the same width as the width of the main portions) as previously described.
  • the width of the base portions 11 f may be smaller than or larger than the standard width.
  • the width of the base portions 11 f may be the same as the width of the base-side wider portions 11 e .
  • the base-side wider portions 11 e may be regarded as extending to the busbars 9 .
  • the piezoelectric body 3 having the top surface 3 a on which the IDT electrode 5 is formed may constitute part of or the entirety of a substrate, for example.
  • the substrate may have any of various configurations, for example, may have a known configuration. Hereafter, examples of the configuration of the substrate are described.
  • FIG. 2 is a sectional view illustrating the configuration of a substrate 13 A as a first example of a substrate.
  • the illustrated cross section corresponds to a cross section taken along line II-II in FIG. 1 .
  • the substrate 13 A includes, for example, a support substrate 15 , an intermediate layer 17 stacked on the top surface of the support substrate 15 , and a piezoelectric body 3 stacked on the top surface of the intermediate layer 17 .
  • the piezoelectric body 3 consists of a piezoelectric film.
  • the words “plate”, “layer”, and “film” are assumed to have the same meaning, unless stated otherwise.
  • the thickness of each layer is constant, for example, regardless of the position in planar directions (directions parallel to the D1-D2 plane).
  • the piezoelectric body 3 is composed of, for example, a single crystal having piezoelectric properties.
  • quartz (SiO 2 ) are examples of materials constituting such a single crystal.
  • the piezoelectric body 3 may be composed of a polycrystalline material. The cut angle, planar shape, and various dimensions of the piezoelectric body 3 may be set as appropriate.
  • a piezoelectric body composed of LT or LN may be composed of a rotated Y-cut X-propagation crystal.
  • the propagation direction of acoustic waves (D1 direction) and the X-axis may substantially coincide with each other (for example, the difference therebetween may be ⁇ 10°).
  • the inclination angle of the Y axis to a normal (D3 direction) to the top surface 3 a of the piezoelectric body 3 may be set as appropriate.
  • the thickness of the piezoelectric body 3 may be, for example, greater than or equal to 0.1p or 0.3p and less than or equal to 2p or 1p. An appropriate combination of these upper and lower limits may be used.
  • the support substrate 15 may, for example, contribute to at least one of the following: increasing the strength of the substrate 13 A, compensating for changes in properties caused by changes in temperature (temperature compensation), and confining acoustic waves to the piezoelectric body 3 .
  • Increased strength may be achieved, for example, by appropriately setting the thickness of the support substrate 15 , which is composed of a material having a certain degree of strength.
  • Temperature compensation may be achieved by, for example, making the coefficient of linear expansion of the support substrate 15 smaller than that of the piezoelectric body 3 .
  • Confinement of acoustic waves may be achieved by, for example, making the acoustic velocity of the support substrate 15 higher than that of the piezoelectric body 3 (and/or the intermediate layer 17 ) and/or by making the acoustic impedance of the support substrate 15 different from that of the intermediate layer 17 .
  • the material and thickness of the support substrate 15 may be set as appropriate in light of the objectives described above.
  • the material of the support substrate 15 may be a semiconductor such as silicon (Si), a single crystal such as sapphire (Al 2 O 3 ), or a ceramic such as sintered aluminum oxide (Al 2 O 3 ).
  • the thickness of the support substrate 15 is, for example, greater than or equal to 1p or 3p.
  • the thickness of the support substrate 15 is, for example, greater than the thickness of the piezoelectric body 3 .
  • the intermediate layer 17 may, for example, contribute to at least one of the following: increasing the bonding strength between the piezoelectric body 3 and the support substrate 15 , and confining acoustic waves to the piezoelectric body 3 .
  • Increased bonding strength may be achieved by, for example, selecting a material for the intermediate layer 17 that has relatively high bonding strength with the piezoelectric body 3 and the support substrate 15 when using a prescribed bonding technique.
  • Confinement of acoustic waves may be achieved, for example, by making the acoustic velocity of the intermediate layer 17 lower than that of the piezoelectric body 3 (and/or support substrate 15 ) and/or by making the acoustic impedance of the intermediate layer 17 different from that of the piezoelectric body 3 (and/or support substrate 15 ).
  • the material and thickness of the intermediate layer 17 may be set as appropriate in light of the objectives described above.
  • the material of the intermediate layer 17 may be silicon oxide (SiO 2 ).
  • the thickness of the intermediate layer 17 may be, for example, greater than or equal to 0.01p or 0.1p, and may be less than or equal to 2p, 1p, or 0.5p. An appropriate combination of these upper and lower limits may be used.
  • the thickness of the intermediate layer 17 is smaller than the thickness of the support substrate 15 , for example.
  • the thickness of the intermediate layer 17 may be smaller than, equal to, or greater than the thickness of the piezoelectric body 3 .
  • the intermediate layer 17 may be a low acoustic velocity layer having a lower acoustic velocity than the piezoelectric body 3
  • the support substrate 15 may be a high acoustic velocity layer having a higher acoustic velocity than the piezoelectric body 3 . In this way, for example, leaking of acoustic waves from the piezoelectric body 3 can be reduced.
  • acoustic velocity used here may be, for example, the transverse acoustic velocity determined by the physical properties of each material. In other words, unlike the acoustic velocities used to distinguish the above-described first to fourth regions R 1 to R 4 from each other, the effect of the IDT electrode 5 may be ignored.
  • the transverse acoustic velocity is obtained by taking the square root of the elastic modulus divided by the density.
  • an acoustic velocity of the piezoelectric body 3 to be compared to the acoustic velocity of the intermediate layer 17 and the support substrate 15 may be the acoustic velocity in the third regions R 3 of the acoustic waves of the mode being utilized instead of the transverse acoustic velocity.
  • the acoustic velocity of the intermediate layer 17 and/or the support substrate 15 may be the acoustic velocity of bulk waves of a mode that has a relatively greater effect on leakage of the energy of acoustic waves of the utilized mode.
  • the combination of the material of the intermediate layer 17 serving as a low acoustic velocity layer and the material of the support substrate 15 serving as a high acoustic velocity layer may be chosen as appropriate.
  • the combination of these materials may be the combination of SiO 2 and Si described above.
  • a layer that improves the bonding strength between the intermediate layer 17 and the piezoelectric body 3 may be provided and/or a relatively thin layer that improves the bonding strength between the intermediate layer 17 and the support substrate 15 may be provided.
  • FIG. 3 is a sectional view illustrating the configuration of a substrate 13 B as a second example of a substrate.
  • the illustrated cross section corresponds to a cross section taken along line II-II in FIG. 1 .
  • the substrate 13 B includes a multilayer film 19 instead of the intermediate layer 17 in the previously described substrate 13 A.
  • the multilayer film 19 includes two or more (six in the illustrated example) acoustic films (first films 21 A and second films 21 B).
  • first films 21 A and second films 21 B the materials of acoustic films that are adjacent to each other in the stacking direction (stacked without another acoustic film therebetween) are different from each other.
  • adjacent acoustic films have different acoustic impedances from each other. As a result, for example, the reflectivity of acoustic waves at the boundary between two different layers is comparatively high.
  • the combination of the intermediate layer 17 and the support substrate 15 in the substrate 13 A in FIG. 2 may be considered as a type of multilayer film.
  • a multilayer film including the support substrate 15 may be defined in the substrate 13 B in FIG. 3 .
  • the number of different types of acoustic film materials and the number of acoustic films in the multilayer film 19 may be set as appropriate.
  • the two types of acoustic films (first films 21 A and second films 21 B) are stacked in an alternating manner for three or more layers (more specifically, six layers).
  • the materials of the acoustic films may be chosen as appropriate.
  • the material of the first films 21 A may be silicon dioxide (SiO 2 ).
  • the material of the second films 21 B may be tantalum pentoxide (Ta 2 O 5 ), hafnium oxide (HfO 2 ), zirconium dioxide (ZrO 2 ), titanium oxide (TiO 2 ), magnesium oxide (MgO), or silicon nitride (Si 3 N 4 ).
  • the first films 21 A have a lower acoustic impedance than the second films 21 B, for example.
  • the thicknesses of the acoustic films may be set as appropriate, for example, the description of the thickness of the intermediate layer 17 above may be applied.
  • the acoustic films may constitute low-acoustic-velocity films and high-acoustic-velocity films, similarly to the intermediate layer 17 and the support substrate 15 of the substrate 3 A in FIG. 2 .
  • the first films 21 A may be composed of a material (for example, SiO 2 or Ta 2 O 5 ) having a lower acoustic velocity than the piezoelectric body 3 .
  • the second films 21 B may be composed of a material (for example, Si 3 N 4 ) having a higher acoustic velocity than the piezoelectric body 3 .
  • a substrate containing the piezoelectric body 3 may have any of various configurations other than the above examples.
  • the substrate may be almost entirely constituted by the piezoelectric body 3 .
  • the piezoelectric body 3 may be relatively thick.
  • the substrate may include a cavity below a relatively thin (for example, a thickness less than or equal to 2p or 1p) piezoelectric body 3 .
  • the substrate may also include, separately from the support substrate 15 , a high acoustic velocity layer that stacked on the bottom surface of the intermediate layer 17 serving as a low acoustic velocity layer in the substrate 13 A in FIG. 2 .
  • confinement of acoustic waves may be realized by stacking a high acoustic velocity layer on the bottom surface of the piezoelectric body 3 .
  • the acoustic wave device 1 may include an insulating protective film covering the top surface 3 a of the piezoelectric body 3 from above the conductor layer including the IDT electrode 5 .
  • the protective film may, for example, contribute to reducing corrosion of the conductor layer and/or contribute to temperature compensation.
  • SiO 2 , Si 3 N 4 and Si can be used as the material of the protective film.
  • the protective film may be a multilayer body consisting of these materials.
  • the device 1 may also include an additional film stacked on the top surface or the bottom surface of the IDT electrode 5 .
  • the additional film for example, is stacked on part of or the entirety of the IDT electrode 5 and has a shape that fits within the IDT electrode 5 in planar perspective view.
  • Such an additional film is composed of an insulating or metal material having different acoustic properties from the material of the IDT electrode 5 , for example, and contributes to improving the reflection coefficient of acoustic waves.
  • the device 1 may be packaged as appropriate.
  • the following can be given as examples of the configuration of the package.
  • the acoustic wave device 1 includes the piezoelectric body 3 and the IDT electrode 5 .
  • the piezoelectric body 3 has the first surface (top surface 3 a ).
  • the IDT electrode 5 is positioned on the top surface 3 a .
  • the IDT electrode 5 includes multiple first electrode fingers 11 A and multiple second electrode fingers 11 B.
  • the multiple second electrode fingers 11 B are connected to a different potential from the multiple first electrode fingers 11 A and are arranged so as to alternate with the multiple first electrode fingers 11 A in the propagation direction of acoustic waves (D1 direction).
  • the device 1 includes the crossing region R 0 in which the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B overlap in the acoustic wave propagation direction.
  • the crossing region R 0 includes the first to third regions R 1 to R 3 (here the +D2 side is taken as an example).
  • the first region R 1 is positioned at the tip sides of the multiple first electrode fingers 11 A.
  • the second region R 2 is positioned more centrally than the first region R 1 in the direction in which the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B extend (D2 direction) and has a higher acoustic velocity than the first region R 1 .
  • the third region R 3 is positioned more centrally than the second region R 2 and has a higher acoustic velocity than the second region R 2 .
  • spurious can be reduced.
  • the first region R 1 which has a low acoustic velocity, is formed at the end of the crossing region R 0 in the D2 direction, and therefore a piston mode (or a similar mode, the same applies hereinafter) can be used.
  • transverse mode spurious can be reduced.
  • the second region R 2 which has a higher acoustic velocity than first region R 1 and a lower acoustic velocity than the third region R 3 , is formed, and as a result, spurious can be further reduced. The applicant has confirmed this effect through actual measurements on test pieces and simulation calculations, and a number of examples will be described hereafter.
  • the width (standard width) of the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B in the third region R 3 are used for comparison.
  • the first region R 1 may include wider portions (in the first region R 1 on the +D2 side, the tip-side wider portions 11 a of the first electrode fingers 11 A and the base-side wider portions 11 e of the second electrode fingers 11 B) in both the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B.
  • the second region R 2 may include the wider portions in one out of the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B (in the second region R 2 on the +D2 side, the second electrode fingers 11 B) and does not need to include the wider portions in the other one out of the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B (in the second region R 2 on the +D2 side, the first electrode fingers 11 A).
  • the ⁇ D2-side end portions of the tip-side wider portions 11 a of the first electrode fingers 11 A and the ⁇ D2-side end portions of the base-side wider portions e of the second electrode fingers 11 B are at different positions in the D2 direction.
  • the reflection positions and/or diffraction positions of acoustic waves propagating in the transverse direction vary depending on the position in the D1 direction. Consequently, the probability of transverse acoustic waves strengthening each other is reduced and spurious is reduced.
  • the second region R 2 which has a higher acoustic velocity than the first region R 1 and a lower acoustic velocity than the third region R 3 , is easier to realize.
  • the width of the electrode fingers 11 in the second region R 2 has a value that lies between the width of the electrode fingers 11 in the first region R 1 and the width of the electrode fingers 11 in the third region R 3 may be considered (this is also included in the technology according to the present disclosure).
  • achieving such a width for the second region R 2 may be difficult due to the machining accuracy with respect to the width of the electrode fingers 11 .
  • the second region R 2 can be realized in this case as well.
  • the tip-side wider portions (tip-side wider portions 11 a ) of the multiple first electrode fingers 11 A may be located in the first region R 1 on the +D2 side, and do not need to be located in the second region R 2 on the +D2 side.
  • the wider portions (base-side wider portions 11 e ) located at the bases of the multiple second electrode fingers 11 B may be located in the first region R 1 on the +D2 side and in the second region R 2 on the +D2 side. In other words, the base-side wider portions 11 e may extend further toward the center of the crossing region R 0 in the D2 direction than the tip-side wider portions 11 a.
  • the cross-sectional area of the electrode fingers 11 can be secured more easily on the side near the busbar 9 . As a result, transmission of signals and/or heat between the busbars 9 and the electrode fingers 11 is facilitated.
  • the acoustic wave device 1 may further include the fourth region R 4 .
  • the fourth region R 4 may be positioned more centrally in the D2 direction than the third region R 3 , and may have a higher acoustic velocity than the third region R 3 .
  • spurious can be further reduced.
  • the applicant has confirmed this effect through actual measurements on test pieces and simulation calculations, and a number of examples will be described hereafter.
  • the reason why spurious is reduced by the formation of the fourth region R 4 is that, for example, the effect of reducing transverse mode spurious is multiplied by the formation of multiple regions in the acoustic velocity profile that contribute to the realization of the piston mode.
  • the length (width) of the fourth region R 4 in the direction in which the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B extend (D2 direction) may be less than 1.5 times the pitch p of the multiple first electrode fingers 11 A and the multiple second electrode fingers 11 B.
  • the characteristics of the acoustic wave device 1 are improved.
  • the applicant has confirmed this effect through actual measurements on test pieces and simulation calculations, and a number of examples will be described hereafter.
  • the reason why the characteristics are improved by the width of the fourth region R 4 being less than 1.5p, is that, for example, the smaller width of the fourth region R 4 allows the width of the third regions R 3 , which are responsible for the basic characteristics, to be more easily secured.
  • transverse mode acoustic waves with a wavelength (2p) equivalent to that of the acoustic waves that are intended to be utilized do not fit into the fourth region R 4 .
  • the acoustic wave device 1 may further include a low-acoustic-velocity film (intermediate layer 17 in FIG. 2 or first films 21 A in FIG. 3 ) and a high-acoustic-velocity film (support substrate 15 in FIG. 2 or second films 21 B in FIG. 3 ).
  • the low-acoustic-velocity film is stacked on the opposite side of the piezoelectric body 3 , which is composed of a piezoelectric film, from the top surface 3 a of the piezoelectric body 3 and has a lower acoustic velocity than the piezoelectric body 3 .
  • the high-acoustic-velocity film is stacked on the opposite side of the low-acoustic-velocity film from the piezoelectric body 3 and has a higher acoustic velocity than the piezoelectric body 3 .
  • FIG. 4 is a plan view illustrating the configuration of an acoustic wave device 201 according to a Second Embodiment (hereinafter, may be referred to as a “device 201 ”).
  • FIG. 5 is a sectional view taken along line V-V in FIG. 4 .
  • FIG. 4 for convenience, the top surfaces (i.e., non-sectional surfaces) of a first additional film 23 A and a second additional film 23 B, which are described below, are shaded with hatching.
  • some of the symbols relating to an IDT electrode 205 are affixed to areas that are not visible because the areas are covered by the additional films. Unlike in the following description, the additional films may be considered to be part of the IDT electrode 205 .
  • the acoustic velocity of the acoustic waves was described as being affected by the mass of members (for example, the IDT electrode 5 ) located on the top surface 3 a of the piezoelectric body 3 .
  • the mass on the top surface 3 a is made different in the first to fourth regions R 1 to R 4 by changing the width of the electrode fingers 11 , and in this way, the velocity profile in FIG. 1 is realized.
  • the velocity profile in FIG. 1 is realized by providing additional films (first additional film 23 A and second additional film 23 B) stacked on parts of the electrode fingers 11 , rather than by varying the width of the electrode fingers 11 . This is described in more detail below.
  • the IDT electrode 205 includes a pair of comb electrodes 207 , similarly to the IDT electrode 5 in the First Embodiment.
  • the pair of comb electrodes 207 include busbars 9 and multiple electrode fingers 211 (multiple first electrode fingers 211 A and multiple second electrode fingers 211 B).
  • the multiple electrode fingers 211 are different from the multiple electrode fingers 11 in the First Embodiment in that the electrode fingers 211 extend with a constant width along their entire length.
  • the first additional film 23 A and the second additional films 23 B are stacked on the parts of the electrode fingers 211 that corresponds to the base portions 11 f of the electrode fingers 11 in the First Embodiment. This corresponds to making the width of the base portions 11 f equal to the width of the base-side wider portions 11 e in the First Embodiment.
  • the parts corresponding to the base portions 11 f do not need to be provided with the first additional film 23 A and/or the second additional film 23 B.
  • the first additional film 23 A and the second additional film 23 B are stacked on the busbars 9 . Unlike in the illustrated example, the first additional film 23 A and/or the second additional film 23 B do not need to be stacked on the busbars 9 .
  • the first and second additional films 23 A and 23 B may be provided or not provided at parts corresponding to the busbars 9 and the base portions 11 f so that the acoustic velocity of the busbar regions RB is lower than the acoustic velocity of the gap regions RG.
  • the additional film was also mentioned in the First Embodiment.
  • the description of the additional film in the First Embodiment may be applied to this embodiment.
  • the additional film may be positioned on the bottom surface of the IDT electrode 5 .
  • the specific material and thickness of the additional film may be chosen as appropriate.
  • examples of such a material include Ta 2 O 5 , TaSi 2 , W 5 Si 2 , WC, and TiN.
  • the thickness of the additional film may be, for example, greater than or equal to 0.01p and less than or equal to 0.2p.
  • the crossing region R 0 of the acoustic wave device 201 includes the first to third regions R 1 to R 3 . Therefore, substantially the same effect as in the First Embodiment is achieved. For example, spurious can be reduced.
  • the first region R 1 on the +D2 side may include an additional film (second additional film 23 B) that is stacked on both the multiple first electrode fingers 211 A and the multiple second electrode fingers 211 B.
  • the second region R 2 on the +D2 side may include the second additional film 23 B stacked on one out of the multiple first electrode fingers 211 A and the multiple second electrode fingers 211 B (second electrode fingers 211 B), and does not need the second additional film 23 B to be stacked on the other one (first electrode fingers 211 A).
  • the third regions R 3 do not need to include the second additional film 23 B on either the multiple first electrode fingers 211 A or the multiple second electrode fingers 211 B.
  • FIG. 6 is a plan view illustrating the configuration of an acoustic wave device 301 according to a Third Embodiment (hereinafter, may be simply referred to as a “device 301 ”).
  • each comb electrode 307 includes multiple dummy electrodes 25 extending parallel to the multiple electrode fingers 311 from the busbar 9 , unlike in the First Embodiment.
  • the tips of the dummy electrodes 25 of one comb electrode 307 face the tips of the electrode fingers 311 of the other comb electrode 307 across gaps G1.
  • the base portions 311 f of the electrode fingers 311 have a length (in the D2 direction) that is the sum of the length of the gap G1 (in the D2 direction) and the length of the dummy electrode 25 (in the D2 direction).
  • dummy regions RD are formed between the gap regions RG and the busbar regions RB.
  • the acoustic velocity in the dummy regions RD is lower than the acoustic velocity in the gap regions RG and higher than the acoustic velocity in the busbar regions RB, if additional films are not considered.
  • the relationship may differ depending on additional films. For the sake of convenience, additional films are not considered in the description of this embodiment.
  • the shape of the dummy electrodes 25 may be set as appropriate.
  • the dummy electrodes 25 are roughly shaped so as to have a constant width and protrude in a direction perpendicular to the propagation direction of acoustic waves.
  • the width of the dummy electrodes 25 is the same as the standard width of the electrode fingers 311 (width of the tip-side main portions 19 a and so on).
  • the acoustic velocity of the dummy regions RD is equal to the acoustic velocity of the third regions R 3 .
  • the width of the dummy electrodes 25 may be greater than or smaller than the standard width.
  • the width of the dummy electrodes may be the same as the width of the tip-side wider portions 311 a .
  • the width of the base portions 311 f may be the same as or different from the width of the tip-side wider portions 311 a .
  • the acoustic velocity in the dummy regions RD may be lower than or higher than the acoustic velocity in the third regions R 3 .
  • the acoustic velocity in the dummy regions RD may be equal to the acoustic velocity in the first regions R 1 or the second regions R 2 .
  • the width of the dummy electrodes 25 may vary with the position in the D2 direction.
  • the width of the dummy electrodes 25 may be larger at the tip or the base.
  • the dummy regions RD may include two or more regions with different acoustic velocities from each other.
  • the IDT electrode 305 may include multiple first dummy electrodes 25 A and multiple second dummy electrodes 25 B.
  • the multiple first dummy electrodes 25 A are connected to the same potential (same busbar 9 ) as the multiple first electrode fingers 311 A, and their tips face the tips of the multiple second electrode fingers 311 B across the gaps G1.
  • the multiple second dummy electrodes 25 B are connected to the same potential (same busbar 9 ) as the multiple second electrode fingers 311 B, and their tips face the tips of the multiple first electrode fingers 311 A across the gaps G1.
  • the number of regions with different acoustic velocities is increased outside the crossing region R 0 .
  • the number of items that can be adjusted in the velocity profile is increased.
  • the mass on the top surface 3 a of the piezoelectric body 3 may be varied by making the thickness of the IDT electrode greater and/or smaller in parts of the IDT electrode, and the first to fourth regions R 1 to R 4 may be realized in this way.
  • changes in thickness due to the additional films in the third embodiment may be realized as changes in the thickness of the IDT electrode itself.
  • the second regions R 2 were realized by providing wider portions or additional films (mass-changed portions) at every other electrode finger in the array of multiple first electrode fingers and multiple second electrode fingers.
  • the second regions R 2 may be realized by setting the width of all the electrode fingers to be between the width of the electrode fingers in the first regions R 1 and the width of the electrode fingers in the third regions R 3 . This also applies to other mass-changed portions such as additional films.
  • the technique of providing a mass-changed portion (for example, a wider portion) at every other electrode finger in the second regions R 2 may also be applied in regions other than the second regions R 2 .
  • the technique of providing a mass-changed portion at every other electrode finger may be applied not only when increasing the mass with respect to the reference portions of the electrode fingers (for example, the main portions located in the third regions), but also when decreasing the mass.
  • the narrower portions 11 c may be provided at every other electrode finger.
  • the mass-changed portions may be provided at every third or higher electrode fingers in the array of electrode fingers, rather than at every other electrode finger.
  • the electrode fingers may be provided with wider portions and additional films that are stacked on the wider portions and are not stacked on the main portions.
  • narrower portions may be provided without providing wider portions, and additional films may be provided only in the first and second regions R 1 and R 2 out of the first to fourth regions R 1 to R 4 .
  • the second regions R 2 may be omitted.
  • the length of the tip-side wider portions 11 a and the length of the base-side wider portions 11 e may be the same.
  • the fourth region R 4 may be omitted.
  • the tip-side main portion 11 b and the base-side main portion 11 d may be connected and configured as a single main portion without providing the narrower portion.
  • the first to fourth regions R 1 to R 4 in the embodiments are examples of first to fourth regions in the present disclosure.
  • the third region R 3 may be taken as an example of the second region and the fourth region R 4 as an example of the third region.
  • two adjacent regions, out of the first to fourth regions R 1 to R 4 may be regarded as an example of one region out of the first to third regions.
  • a fifth region that has a higher acoustic velocity than the second region R 2 and a lower acoustic velocity than the third region R 3 may be provided between the second region R 2 and the third region R 3 .
  • the second region R 2 and the fifth region may be regarded as an example of the second region, or the fifth region and the third region R 3 may be regarded as an example of the third region.
  • three or more types of regions were provided so that the acoustic velocity increases toward the center in the D2 direction.
  • at least one or more types of regions may be inserted that do not follow the relationship that the acoustic velocity increases toward the center in the D2 direction.
  • Such regions may be used, for example, to fine tune the characteristics of the acoustic wave device.
  • a generic concept that three or more types of regions having different acoustic velocities from each other are provided within the crossing region R 0 can be extracted from the present disclosure.
  • providing three or more types of regions so that the acoustic velocity increases toward the center in the D2 direction is not essential.
  • Acoustic wave devices may be used in various forms such as resonators and filters.
  • example uses of acoustic wave devices will be described. Specifically, the description is generally given in the following order.
  • FIG. 7 is a plan view illustrating the configuration of a resonator 31 .
  • the resonator 31 includes, for example, the piezoelectric body 3 (refer to FIG. 2 and so on), as well as the IDT electrode 5 and a pair of reflectors 35 located on the top surface 3 a of the piezoelectric body 3 .
  • the resonator 31 may be regarded as including the acoustic wave device 1 according to the First Embodiment, or may be regarded as being included in the device 1 .
  • the resonator 31 also includes piezoelectric body 3 (and other layers that affect acoustic waves), as described above. For convenience, however, the combination of the IDT electrode 5 and the pair of reflectors 35 may be referred to as the resonator 31 .
  • the pair of reflectors 35 consists of the same conductor layer as the conductor layer constituting the IDT electrode 5 , for example. In a form in which additional films overlap all or parts of the IDT electrode 5 , additional films may be provided that overlap all or parts of the reflectors 35 .
  • the pair of reflectors 35 are positioned on both sides of the IDT electrode 5 in the propagation direction of acoustic waves. Each reflector 35 may be electrically floating or supplied with a reference potential, for example.
  • Each reflector 35 is formed in the shape of a lattice, for example.
  • each reflector 35 includes a pair of busbars 37 facing each other and multiple strip electrodes 39 extending between the pair of busbars 37 .
  • the multiple strip electrodes 39 may be actually provided in a greater number than is illustrated.
  • the busbars 37 generally have substantially the same configuration as the busbars 9 of the IDT electrode 5 , for example, and the description of the busbars 9 may be applied to the busbars 37 .
  • the busbars 37 are serially arranged with respect to the busbars 9 in the propagation direction of acoustic waves, for example.
  • the width of the busbars 37 is identical to the width of the busbars 9 .
  • the width of busbars 37 may be different from the width of the busbars 9 .
  • the busbars 37 may be at different positions in the D2 direction than the busbars 9 .
  • the busbars 37 may be inclined with respect to the propagation direction of acoustic waves similarly to the busbars 9 or may be parallel to the propagation direction of acoustic waves.
  • the schematic configuration of the multiple strip electrodes 39 is substantially the same as the schematic configuration of the electrode fingers 11 of the IDT electrode 5 , except that the strip electrodes 39 span between the pair of busbars 37 .
  • the description of electrode fingers 11 may be applied to the strip electrodes 39 as appropriate.
  • the multiple strip electrodes 39 are arranged in the propagation direction of acoustic waves so as to follow the arrangement of the multiple electrode fingers 11 .
  • the pitch of the multiple strip electrodes 39 and the pitch of the electrode fingers 11 adjacent to the reflectors 35 and the strip electrodes 39 adjacent to the IDT electrode 5 are identical to the pitch of the multiple electrode fingers 11 , for example.
  • the strip electrodes 39 are shaped so as to include wider portions 39 b in regions obtained by extending the first regions R 1 (refer to FIG. 1 and so on) in the D1 direction.
  • the width of the portions other than the wider portions 39 b is identical to the standard width of the electrode fingers 11 (width of the tip-side main portions 11 b and so on), for example.
  • the width of the wider portions 39 b is identical to the width of the tip-side wider portions 11 a and base-side wider portions 11 e of the electrode fingers 11 , for example.
  • the regions obtained by extending the crossing region R 0 to the reflectors 35 may each include three or more types of regions having different acoustic velocities from each other.
  • the multiple strip electrodes 39 may be configured such that two types of wider portions having different lengths from each other in the D2 direction are arranged in an alternating manner, similarly to the electrode fingers 11 .
  • the multiple strip electrodes 39 may include narrower portions in the center in the D2 direction, similarly to the electrode fingers 11 .
  • the two types of wider portions and the narrower portion may be used in combination with each other.
  • the regions obtained by extending the crossing region R 0 to the reflectors 35 may have a constant acoustic velocity.
  • the strip electrodes 39 may have a constant width throughout their length.
  • the number and type of regions relating to acoustic velocity in the IDT electrode 5 and the number and type of regions relating to acoustic velocity in the reflectors 35 may be different from each other (illustrated example) or the same.
  • the method for varying the mass on the top surface 3 a of the piezoelectric body 3 is not limited to a method in which the width of the strip electrodes 39 is varied, and various other methods may be used. In one resonator 31 , the same method (illustrated example) or different methods may be used to vary the mass in the IDT electrode 5 and the reflectors 35 .
  • FIG. 8 is a circuit diagram schematically illustrating the configuration of a splitter 101 (for example, a duplexer).
  • the comb electrodes 7 are each schematically illustrated in the shape of a two-pronged fork, and the reflectors 35 are each represented by a single line bent at both ends, as indicated by the symbols in the upper left corner of the figure.
  • the splitter 101 includes, for example, a transmission filter 109 that filters a transmission signal from a transmission terminal 105 and outputs the filtered transmission signal to an antenna terminal 103 , and a reception filter 111 that filters a reception signal from the antenna terminal 103 and outputs the filtered reception signal to a pair of reception terminals 107 .
  • the transmission filter 109 is configured, for example, as a ladder filter consisting of multiple resonators 31 (series resonators 31 S and parallel resonators 31 P) connected to each other in a ladder configuration.
  • the transmission filter 109 includes multiple (or just one) series resonators 31 S connected in series with each other between the transmission terminal 105 and the antenna terminal 103 , and multiple (or just one) parallel resonators 31 P (parallel arms) connecting the series line (series arm) to a reference potential part (symbol omitted).
  • the reception filter 111 includes, for example, a resonator 31 and a multi-mode filter (which is assumed to include a dual-mode filter) 113 .
  • the multi-mode filter includes a dual-mode filter.
  • the multi-mode filter 113 includes multiple (three in the illustrated example) IDT electrodes 5 arranged in the propagation direction of acoustic waves and a pair of reflectors 35 disposed on both sides of the IDT electrodes.
  • At least one of the multiple resonators of the transmission filter 109 may include the acoustic wave device 1 (IDT electrode 5 ) according to the embodiment.
  • the transmission filter 109 includes the device 1 and one or more other IDT electrodes (in the illustrated example, the other IDT electrodes are also the IDT electrode 5 according to the First Embodiment) located on the top surface 3 a of the piezoelectric body 3 of the device 1 and connected to the one IDT electrode 5 in a ladder configuration to form a ladder filter.
  • At least one of the multiple IDT electrodes of the multi-mode filter 113 may include the acoustic wave device 1 (IDT electrode 5 ) according to the embodiment.
  • the multi-mode filter 113 includes the device 1 and one or more other IDT electrodes (in the illustrated example, the other IDT electrodes are also the IDT electrode 5 according to the First Embodiment) located on the top surface 3 a of the piezoelectric body 3 of the device 1 and arranged in the propagation direction of acoustic waves with respect to the one IDT electrode 5 to form a multi-mode filter.
  • Each of the splitter 101 , the transmission filter 109 (ladder filter), the reception filter 111 , and the multi-mode filter 113 may be considered to include the device 1 according to the First Embodiment, or may be considered to be included in the device 1 .
  • the multiple IDT electrodes 5 (and reflectors 35 ) of the splitter 101 may be provided on a single piezoelectric body 3 (substrate) or provided so as to be distributed over two or more piezoelectric bodies 3 .
  • the multiple resonators 31 constituting the transmission filter 109 may be located on the same piezoelectric body 3 .
  • the resonator 31 and the multi-mode filter 113 constituting the reception filter 111 may be provided on the same piezoelectric body 3 , for example.
  • the transmission filter 109 and the reception filter 111 may be provided on the same piezoelectric body 3 , for example, or on different piezoelectric bodies 3 from each other.
  • the multiple series resonators 31 S may be provided on the same piezoelectric body 3
  • the multiple parallel resonators 31 P may be provided on another piezoelectric body 3 .
  • FIG. 9 is a block diagram illustrating main parts of a communication device 151 as an example use of the acoustic wave device 1 .
  • the communication device 151 performs wireless communication using radio waves and includes the splitter 101 .
  • a transmission information signal TIS which contains information to be transmitted, is modulated and raised in frequency (converted to a radio-frequency signal having a carrier frequency) by a radio frequency integrated circuit (RF-IC) 153 , and becomes a transmission signal TS.
  • Unwanted components outside a transmission passband are removed from the transmission signal TS by a bandpass filter 155 , and the resulting transmission signal TS is then amplified by an amplifier 157 and input to the splitter 101 (transmission terminal 105 ).
  • the splitter 101 (transmission filter 109 ) removes unwanted components outside the transmission passband from the input transmission signal TS, and then outputs the transmission signal TS resulting from the removal from the antenna terminal 103 to an antenna 159 .
  • the antenna 159 converts the input electrical signal (transmission signal TS) into a radio signal (radio waves) and transmits the radio signal.
  • a radio signal (radio waves) received by the antenna 159 is converted into an electrical signal (reception signal RS) by the antenna 159 and input to the splitter 101 (antenna terminal 103 ).
  • the splitter 101 removes unwanted components outside a reception passband from the input reception signal RS and outputs the resulting reception signal RS from the reception terminal 107 to an amplifier 161 .
  • the output reception signal RS is amplified by the amplifier 161 , and unwanted components outside the reception passband are removed by a bandpass filter 163 .
  • the reception signal RS is then reduced in frequency and demodulated by the RF-IC 153 , and becomes a reception information signal RIS.
  • the transmission information signal TIS and the reception information signal RIS may be low-frequency signals (baseband signals) containing appropriate information, for example, analog or digitized audio signals.
  • the radio signal passband may be set as appropriate and may conform to any of various known standards.
  • the modulation method may be phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more of these methods.
  • the direct conversion method is illustrated as an example, other types of circuit may be used as appropriate, for example, a double superheterodyne type circuit.
  • FIG. 9 is a diagram schematically illustrating only the main parts, and a low-pass filter, an isolator, and so on may be added at appropriate positions, and the positions of amplifiers and so on may be changed.
  • the acoustic wave device 1 may be used in various forms other than those described above.
  • the acoustic wave device 1 may be used in a two-port resonator or in a transversal filter.
  • the effect of the acoustic wave device 1 according to the embodiment was confirmed by measuring the characteristics of test pieces of the resonator 31 according to the embodiment ( FIG. 7 ) and by calculating the characteristics of the resonator 31 through simulation. A number of examples are described below.
  • FIG. 10 is a diagram illustrating the characteristics of resonators according to a First Comparative Example and a First Practical Example.
  • FIG. 10 the horizontal axis represents frequency.
  • the vertical axis represents phase of impedance.
  • a line LC 1 represents a characteristic of the First Comparative Example.
  • a line LE 1 represents a characteristic of the First Practical Example.
  • FIG. 10 is obtained by measuring the characteristics of test pieces.
  • the resonator 31 has a resonant frequency at which the absolute value of impedance is a minimum value and an anti-resonant frequency at which the absolute value of impedance is a maximum value.
  • the closer the phase of the impedance is to 90° the better the characteristic of the resonator 31 is.
  • the range on the horizontal axis roughly corresponds to the range between the resonant frequency and the anti-resonant frequency.
  • the First Practical Example is substantially the same as the resonator 31 according to the First Embodiment.
  • the electrode fingers 11 of the IDT electrode 5 and the strip electrodes 39 of the reflectors 35 have a constant width (standard width) along their entire lengths.
  • the First Comparative Example differs from the First Practical Example in that the First Comparative Example includes dummy electrodes. Other parameters are generally the same in the First Comparative Example and the First Practical Example.
  • the number of spurious components and the magnitudes of the spurious components are reduced in the First Practical Example compared to the First Comparative Example.
  • the fact that spurious is reduced by forming the first to fourth regions R 1 to R 4 within the crossing region R 0 was confirmed by actual measurements.
  • the configuration of the reflectors 35 of the First Practical Example is substantially the same as the configuration illustrated in FIG. 7 .
  • FIG. 11 is a diagram illustrating characteristics of resonators according to a Second Comparative Example and the First Practical Example (already described), and is similar to FIG. 10 .
  • FIG. 11 is obtained by measuring the characteristics of test pieces similarly to FIG. 10 .
  • a line LC 2 represents a characteristic of the Second Comparative Example.
  • a line LE 1 represents the characteristic of the First Practical Example and is identical to the line LE 1 illustrated in FIG. 10 .
  • the tip-side wider portions and the base-side wider portions have the same length as each other in the D2 direction.
  • the electrode fingers are not provided with narrower portions.
  • the crossing region includes only two types of (3) regions with different acoustic velocities from each other, similarly to an IDT electrode that uses a general piston mode.
  • the strip electrodes of the reflectors in the Second Comparative Example similarly to the strip electrodes of the reflectors in the First Comparative Example, have a constant width (standard width) along their entire length. Other parameters are generally the same in the First Comparative Example and the First Practical Example.
  • the number of spurious components and the magnitudes of the spurious components are reduced in the First Practical Example compared to the First Comparative Example.
  • the fact that spurious is reduced by forming the first to fourth regions R 1 to R 4 within the crossing region R 0 was confirmed by actual measurements.
  • the previously mentioned parameters listed as being common parameters in the First Comparative Example and the First Practical Example are also common parameters in the Second Comparative Example and the First Practical Example.
  • the width of the gap regions (in the D2 direction) in the Second Comparative Example is the same as the width of the gap regions in the First Practical Example.
  • the other parameters of the Second Comparative Example are listed below.
  • FIG. 12 is a diagram illustrating the characteristics of resonators according to the First Comparative Example and the Second Comparative Example (already described) and a Second Practical Example, and is similar to FIG. 10 .
  • FIG. 12 was obtained by performing simulation calculations, unlike FIGS. 10 and 11 .
  • lines LC 1 and LC 2 represent the characteristics of the first and Second Comparative Examples.
  • a line LE 2 represents a characteristic of the Second Practical Example.
  • the same symbols (LC 1 and LC 2 ) as in FIG. 10 and FIG. 11 are attached to the lines representing the characteristics of the first and Second Comparative Examples.
  • the Second Practical Example is the same as the First Practical Example except that the narrower portions 11 c are not provided.
  • the crossing region does not include the fourth region R 4 , but does include 3 types of (5) regions (corresponding to first to third regions R 1 to R 3 ) that have different acoustic velocities from each other.
  • the rest of the configuration of the Second Practical Example is substantially the same as that of the First Practical Example.
  • the magnitudes of spurious components are reduced in the Second Practical Example compared to the First and Second Comparative Examples.
  • simulation calculations confirmed that spurious is reduced not only by forming regions corresponding to the first regions R 1 and the third regions R 3 in the crossing region R 0 , but also by forming second regions R 2 (or, from another perspective, without forming the fourth region R 4 ).
  • FIG. 13 is a diagram illustrating the characteristics of resonators according to the First Comparative Example and the Second Comparative Example (already described) and a Third Practical Example, and is similar to FIG. 10 .
  • FIG. 13 is obtained by performing simulation calculations similarly to FIG. 12 .
  • lines LC 1 and LC 2 represent the characteristics of the first and Second Comparative Examples and are identical to lines LC 1 and LC 2 in FIG. 12 .
  • a line LE 3 represents a characteristic of the Third Practical Example.
  • the length of the base-side wider portions 11 e (in the D2 direction) is the same as the length of the tip-side wider portions 11 a in the First Practical Example.
  • the crossing region does not include second regions R 2 , but includes 3 types of (5) regions (corresponding to first regions R 1 , third regions R 3 , and fourth region) that have different acoustic velocities from each other.
  • the rest of the configuration of the Third Practical Example is substantially the same as that of the First Practical Example.
  • the magnitudes of spurious components are reduced in the Third Practical Example compared to the First and Second Comparative Examples.
  • simulation calculations confirmed that spurious is reduced not only by forming regions corresponding to the first regions R 1 and the third regions R 3 in the crossing region R 0 , but also by forming a fourth region R 4 (or, from another perspective, without forming the second regions R 2 ).
  • FIG. 14 illustrates the characteristics of resonators according to Fourth to Seventh Practical Examples, and is similar to FIG. 10 .
  • FIG. 14 is obtained by performing simulation calculations similarly to FIG. 12 .
  • lines LE 4 , LE 5 , LE 6 , and LE 7 represent the characteristics of the Fourth, Fifth, Sixth, and Seventh Practical Examples.
  • the Fourth to Seventh Practical Examples are examples in which the width (length in the D2 direction) of the fourth region R 4 is different from that in the First Practical Example. Specifically, the widths of the fourth region R 4 are listed below.
  • the spurious is generally smaller, the smaller the width is. Since the lines LE 4 to LE 7 overlap each other in FIG. 14 making comparison difficult, the phase (°) of the impedance in each example for spurious S1 to S4 in the figure are listed below. The larger the value listed below, the smaller the spurious.

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